Traditional serrated adenoma with BRAF mutation is associated with synchronous/metachronous BRAF-mutated serrated lesions

Aims: To determine whether traditional serrated adenoma (TSA) results in an increased risk of developing subsequent serrated polyps or colorectal cancer (CRC). Methods and results: We recruited 111 patients with an index TSA, and analysed the pathological and molecular features of their synchronous/metachronous serrated lesions. Fifty hyperplastic polyps, 14 sessile serrated adenomas, an additional 27 TSAs and 17 CRCs were identified from 46 patients. Twenty-seven percent of TSAs showed a precursor serrated polyp in the periphery and were strongly correlated with BRAF mutation (P < 0.001). Serrated polyps occurred more commonly in patients with BRAF-mutated index TSAs than in patients with KRAS-mutated index TSAs. BRAF-mutated index TSAs were strongly associated with a right-sided location and BRAF mutation of synchronous/metachronous serrated polyps (P = 0.013 and P = 0.005, respectively). The 17 CRCs occurred more frequently in women, and were characterized by a high BRAF mutation rate (59%), a positive CpG island methylator phenotype (59%), and stable or low levels of microsatellite instability (77%). Conclusions: BRAF-mutated TSA is distinct from KRAS-mutated TSA in predisposing to the acquisition of subsequent serrated neoplasia. This indicates the presence of an intestinal field defect in the tumour microenvironment that results in tumour initiation and malignant progression. ? 2016 John Wiley & Sons Ltd.